Our research goals for the coming year are to take advantage of our developing insight into the vitamin D endocrine system and to study certain problems particularly relevant to disorders of calcium metabolism in man. Specifically these include: 1. To continue to apply our assay capability for the simultaneous determination of 25(OH)D, 24,25(OH)2D and 1,25(OH)2D to a number of clinically important vitamin D-related disease states. 2.To initiate clinical trials on the effectiveness of the simultaneous administration of 1,25(OH)2D3 and 24,25(OH)2D3.